The Statistical Analysis and Data Management core will provide the personnel, expertise, and computer resources need for maximal utilization of the data collected by the investigators in this program project. Activities in this core will involve construction and continual updating of data files; data verification and cleaning; selection and application of statistical analyses so as to test stated hypotheses and further investigate the primary issues under study; and interpretation and preparation of results for publication. The principal investigator will oversee all aspects of this process. He will supervise the work of the data manager/statistician; he will be available for consultation on statistical analyses; he will carry out and evaluate results of more advanced analyses such as multi-level modeling and latent curve modeling; and he will assist in the interpretation and description of results. The co-principal investigators will provide experience and expertise in management of large scale longitudinal data sets, background in dealing with data-related issues arising in clinical (e.g., missing data), and experiences in the application and interpretation of statistical methods. A masters level data manager/statistician will maintain the database, provide statistical analyses, and prepare data sets for individual investigators.